Backflow preventing valves are used in irrigation systems and the like to ensure unidirectional fluid flow. In large irrigating systems, various fertilizers and nutrients are typically mixed in with the water that is sprayed or otherwise supplied to crops. As a municipal water main usually provides a common supply of water for all domestic and commercial uses in an area, it is important to prevent the backflow of these fertilizers and nutrients to avoid contaminating the portion of the water used for domestic purposes.
Much effort has been expended in the development of backflow preventing valves which quickly close under conditions which normally cause backflow, such as back pressure or siphonage. As the usual design for a backflow preventing valve includes an inlet passage and an outlet passage, each respectively communicating with an intermediate chamber via an inlet check valve and an outlet check valve, much work has been done to develop the inlet and outlet check valve portions of the backflow preventing valves to ensure a rapid and definite closure for increases in the pressure of the fluid in the outlet passage relative to that in the inlet passage.
For example, in my prior U.S. Pat. No. 3,724,487, I disclosed a backflow preventing valve utilizing a check valve design having a spring urging a piston-type valve seat into a valve port. In my U.S. Pat. No. 4,080,980, I disclosed an improvement to my previous patent in which the inlet and outlet check valves included a booster means cooperating with the spring for forcibly closing the valve without providing an undesirable increased resistance to opening after reaching an initial opened position. The booster means included a cylindrical shaft having rollers biased thereon. When the valve was approaching a closed position, the rollers entered a reduced portion of the shaft which, in combination with a spring biasing the rollers against the shaft, assisted the piston spring in forcibly closing the valve.
Other booster designs have included contoured valve seat stems providing camming surfaces for rollers that are resiliently biased thereagainst. These camming surfaces and rollers maintain a uniform force on the stem after the valve has initially opened and assist the spring in closing the valve. In general, however, the check valve camming arrangements found in the prior art require several moving parts and provide only a limited amount of boost, and are limited in the manner in which the boost is applied.
Developments have also been made in the design of the exhaust valve portion of the backflow preventing valve. The exhaust valve communicates with the inlet passage and intermediate chamber and is used to gate the intermediate chamber fluid to the atmosphere when the pressure in the intermediate chamber rises relative to the inlet passage pressure as the inlet and outlet check valves are closing in a backflow situation. The problem plaguing most exhaust valves is that intermediate chamber fluid is gated to the atmosphere for only transient pressure increases of the intermediate chamber fluid relative to the inlet passage fluid. This pressure increase is caused by displacement of the intermediate chamber fluid as large pressure reductions occur in the inlet passage fluid. This "spitting" by the exhaust valve is undesirable for such momentary pressure increases.
The exhaust valves of the prior art generally have not solved the "spitting" problem, as they generally employ unsophisticated valving arrangements. Even in those exhaust valves which have reduced "spitting", their valving mechanisms are mechanically complicated and susceptible to wear.
Finally, the backflow preventing valves of the prior art are generally bulky devices utilizing large intermediate chambers. The large intermediate chambers have been required because of the relatively large inlet and outlet check valves and exhaust valves used therewith. A more compact design for the check valves and exhaust valves would greatly contribute to reducing the bulkiness of the current backflow preventing designs. A backflow preventing valve utilizing a low-profile valve body could be used in many applications where mounting space tends to be a problem.
Accordingly, it is the principal object of the present invention to simplify the design of the check valve portions of a backflow preventing valve.
It is another object of this invention to control the manner in which the inlet and outlet passages of backflow preventing valves are closed.
It is still another object of this invention to rapidly and efficiently close the check valve portion of a backflow preventing valve.
It is yet another object of this invention to provide a more compact check valve and exhaust valve design for use in a backflow preventing valve.
It is a further object of this invention to provide a highly-durable check valve in a backflow preventing valve.
It is another object of this invention to reduce the spitting action of the exhaust valve portion of a backflow preventing valve by absorbing transitory fluid displacements from the intermediate chamber for large reductions in inlet pressure.
It is still another object of this invention to both simplify the design of the exhaust valve portion of a backflow preventing valve and to prevent the spitting from occurring.
It is a further object of this invention to provide a high-durable exhaust valve in a backflow preventing valve.
It is still another object of this invention to provide a low-profile backflow preventing valve applicable to a wide variety of uses.
It is yet another object of this invention to prevent the contamination of the supply fluid to which a backflow preventing valve is connected.